A new transmitting valve from Russia - the Gi7B
by
Mirko Voznjak, YU1AD and Mike King, G3MY

Issue 55 Six News, November 1997

Mirko, YU1AD writes:

I am writing to give information about a very special
Russian-made transmitting valve, named Gi7B (sounds like some
special event station from Northern Ireland!). This is a
coaxial-type valve, apparently developed to be primarily used in
radar systems, but it is very useful for any frequency from zero
to nearly 3GHz. It is a valve with ceramic insulation (pink
colour!) and has a substantial heatsink at the anode connection.
You can see the valves outline and the set of
characteristic curves, in figure 1. Other electrical data are
given in table 1.

Table 1: Gi7B valve data

Min.

Norm.

Max.

Filament V

12

12.6

13.2

Filament A

1.8

1.92

2.0

Plate V

-

1500

2500

Dissipation W

-

-

350

Eff. cathode current mA

-

400

600

Max usable freq GHz

2.7

-

-

Slope mA/V

20

23

26

Output power W

-

-

350

Cap Gg-k pF

10

11.1

12.2

Cap Ga-k pF

0.055

0.075

0.08

Cap Gg-a pF

4

4.6

5.2

It is a directly heated triode, with the heater connections on
two bottom round-type connectors, so it can be easily connected
with the aid of appropriate shells. Above that is the grid
connection, which fits a brass or bronze machined flange fixed to
the chassis with, say, four M3 screws, giving a very good ground
connection for a grounded grid amplifier. Above that broad round
area, below the heatsink, is a silvered metal connection for the
plate, which could be realised with an appropriate shell.
Naturally, this valve requires forced air cooling, with a good
squirrel fan, to blow the part of the valve which is above the
chassis.

Figure 1 - Gi7B valve outline and
characteristic curves.

Up to this moment it might sound like a fairy tale, until we
discover how cheap and easily obtainable it is. A Yugoslavian
ham, who runs his own trade business, has about 100 of them
available to be sent the UK (note that Mirkos letter was
written in May 97 - Ed).

Figure 3: G3MY's cooling chimney - a flower pot!

The price for each valve is 40 DM, plus p/p. For two valves
you should send a bank cheque (not a personal one please, since
they take quite a long time to clear) for the sterling equivalent
of 100DM (currently about £36). If you order four valves, send
the equivalent of 190DM. This is the limit for one order, since
four well-packed valves weigh 1.85kg which is near the limit for
shipment. If you need more, they will be shipped in two packages.
I am guaranteeing that the business is absolutely legal and
no-one will lose any money. If they are sold out, cheques will be
returned.

Figure 2: The interior of Mike, G3MY's Gi7B amplifier.

With each shipment you will get a photocopy of an article from
the Hungarian magazine Radiotechnika describing a
linear for 144MHz with complete schematics, plus the drawing of a
mounting flange which has to be turned on a lathe. One tip:
after making the flange to fit the grid area of the valve, make a
vertical cut in it and after dropping the valve in put an
appropriate shell around the flange with the facility to tighten
it with an M4 or 4BA screw. That will keep the valve very firmly
in place and ensure solid grounding of the grid.

My power supply is a full wave voltage doubler with 560V AC
giving about 1.35 to 1.4 kV on load. This and size limits me to
the 225W output, but at 2.5kV maximum output before significant
compression appears to be about 560W PEP - well within the
ratings of the valve.

At the price they must be the gift of the century! And they
are rated to 2.5GHz+!

Editors
note:

While we have no reason to doubt the bona
fides of this offer, please note that the UKSMG can
accept no liability for any problems you may have
obtaining or using these valves.